9 Healthy Foods That Can Be Toxic If You Eat Too Much

That saying about enjoying all things in moderation? It doesn't just apply to red wine, fresh bread, or delicious desserts. It counts for clean foods, too. Because whether you're talking about nuts, fish, leafy greens, or whole grains, there's almost always an instance where you can have too much of a good thing. Here are nine great-for-you foods that can be dangerous if you overdo it. (Lose up to 15 pounds WITHOUT dieting with Eat Clean to Get Lean, our 21-day clean-eating meal plan.)

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Brazil nuts

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These giant nuts are known for being the No. 1 source of selenium, a trace element that plays an essential role in reproduction and helping your body fight off infection. In fact, just one Brazil nut can deliver up to 90 mcg of selenium, which is almost twice as much selenium as you need in a day. And a 1-ounce serving (that's six to eight nuts) packs a whopping 777% of your daily selenium needs.

Eating the occasional serving of Brazil nuts is fine, but having them every day could put you at risk for selenium toxicity—which has the potential to cause hair loss, gastrointestinal and neurologic problems, lightheadedness, and even heart attacks or kidney failure. "Keep it to one weekly serving, or just have one or two nuts a few times a week," says registered dietitian Jessica Cording. (Here are 3 surprising bad things that can happen if you eat too many nuts.)

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Spinach, beets, and Swiss chard

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We don't need to remind you that each of these veggies is a nutritional powerhouse. But they're also high in naturally occurring compounds called oxalates. Oxalates actually work as prebiotics to feed the healthy bacteria in your gut. But if you're prone to kidney stones, eating too many high-oxalate foods only makes things worse. "The kidneys are supposed to filter these compounds out. But in someone who is prone to kidney stones, the kidneys have a hard time doing so, which can lead to buildup and the formation of kidney stones," says Cording. (Try these 7 strategies to prevent kidney stones.) In that case, it could be best to avoid foods that are high in oxalates altogether. Talk to your doctor to figure out what's best for you. If you need to cut out high-oxalate foods, a dietitian can help you find lower-oxalate alternatives, like cabbage or cauliflower.

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Canned tuna

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It's cheap, convenient, and packed with protein and those all-important omega-3s. But canned tuna does contain some mercury, which can harm the nervous systems and brains of developing fetuses and young children. Higher amounts of mercury can be poisonous to adults, too (symptoms include numbness or tingling, vision problems, and memory problems). But experts don't know exactly how much mercury-laden tuna you'd need to eat to get sick.

White albacore tuna contains more mercury than light tuna does, and the amount that you can eat depends on your weight. For instance, a 110-pound person should stick to less than 4 ounces of white albacore tuna or 9 ounces of light tuna per week. But a 165-pound person can have 5 ounces of white albacore tuna or 14 ounces of light tuna per week, according to calculations from Consumer Reports. (FYI, a can of tuna is 5 ounces.)

If you're pregnant, breastfeeding, or trying to conceive, stick with the FDA's established guidelines: Enjoy up to 12 ounces per week of lower-mercury seafood, like shrimp, salmon, catfish, or light tuna. For higher-mercury albacore tuna, limit yourself to no more than 6 ounces per week. (And stay away from these 12 fish altogether.)

All three are top sources of iron, which plays an essential role in delivering oxygen to your muscles. And while too little iron can leave you feeling weak and tired, getting too much can lead to liver failure.

Of course, plenty of people struggle to get enough of the mineral in their diets. So iron overload tends to be pretty rare, especially if your only source of iron is food, Cording says. But if you're taking an iron supplement? It might be worth talking to a dietitian. "It's important to know what your needs are and get a handle on how to balance food sources and supplements," says Cording.

Arsenic is a known human carcinogen, and currently, there's no safety threshold for the amount of arsenic in food. But experts, including those at the Environmental Working Group, agree that you don't need to cut brown rice out of your diet completely. Instead, make an effort to eat a variety of whole grains. "If you would normally have brown rice every day, try to alternate with something like quinoa, farro, or millet," Cording says. Keep an eye out for packaged foods that contain rice or rice-based ingredients like brown rice syrup (which is often used to sweeten natural cereals or granola bars), too. It's better to eat those once in a while rather than every day.

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